Multi-scale energy transfers in the near wake of a model wind turbine

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• Oliver Buxton, Imperial
• Wednesday 29 January 2025, 14:00-15:00
• JDB Seminar RM.

If you have a question about this talk, please contact Anna Walczyk.

A composite image of the instantaneous vorticity (ωz) field in the near wake of a model wind turbine operating at a tip speed ratio λ = 6 from two, non-concurrent, fields of view.

Many turbulent flows are forced at multiple length scales, imprinting coherent motions with multiple characteristic frequencies/length scales simultaneously. Examples include flows through a cityscape or a forest but also past a wind turbine where coherent motions are concurrently imparted into the wake by the tower, nacelle, blade-tip vortices etc. In our previous work we developed the multi-scale triple-decomposition of the velocity field into the mean, a sum of various periodic (coherent) motions, and a stochastic fluctuation [1]

u(x, t) = u(x) ΣN i=1˜ui(x, t) u ′′(x, t) (1)

which we subsequently used to develop the multi-scale triple-decomposed kinetic energy budgets for the mean flow, coherent motions, and stochastic turbulent kinetic energy [2]. The energy budget for the coherent motions contains a “new” term, called the triadic production term, that transfers energy from one coherent mode to another under the catalytic action of a third coherent motion in the triad. This triadic production term was observed to lead to the formation of secondary modes in simple, planar multi-scale flows [2]. In this talk we will observe the various coherent motions that exist in a wind-turbine wake (reported in [3]), and how these depend on the turbine operating condition via the tip speed ratio λ = ΩR/U∞. We will also explore the ways in which the various coherent modes in the wake are energised through the framework of the multi-scale triple decomposed coherent kinetic energy budget (reported in [4]). Finally, we will examine the influence of free-stream turbulence on both the coherent modes that are produced within the wake and the energy transfers that yield them.

(1)The formatting of the equation does not display correctly. See the PDF version version of this abstract.

This talk is part of the Engineering Fluids Group Seminar series.

This talk is included in these lists:

• Acoustics Lab Seminars
• Engineering Department Acoustics/Combustion Student seminars
• Engineering Fluids Group Seminar
• JDB Seminar RM

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